1. Field of the Invention
This invention relates to a dyestuff refining system, and, more particularly, it is concerned with a dyestuff refining system capable of continuously supplying refined dyestuff which is suitable for preparing recording liquid (generally called "ink") adapted to ink jet recording, writing implements, and other uses.
2. Description of Prior Art
As the ink to be used for an ink jet recording system which implements recording of information by ejecting ink within a recording head through an ejection orifice by means of vibrations transmitted from a piezo-electric vibrator or other expedients, there have so far been known various dyestuffs and pigments which are dissolved or dispersed in a liquid medium such as water or other, organic solvents. There has also been known use of ink similar to the abovementioned one for those writing implements such as felt tip pens, fountain pens, etc.
One example of general basic ingredients for such ink may comprise principally the following three chief components: water-soluble dyestuff, water as the solvent for the dyestuff, and glycols as a desiccation-preventive agent.
The water-soluble dyestuff usually contains a large amount of inorganic salts such as sodium chloride, sodium sulfate, and so forth. These inorganic salts are the by-products formed in the course of the dye-synthesizing reaction, or are positively added as a salting-out agent, a diluent, or a level-dyeing agent.
When the recording ink is prepared with use of such dyestuff containing such inorganic salts, awkward situations would take place: the inorganic salts lower the dissolution stability of the dyestuff in the ink to bring about agglomeration and sedimentation of the dyestuff. Further, in the ink jet recording heads and writing implements, if and when the ink is evaporated in the vicinity of the ejection orifice causing the liquid composition to change, deposition of the inorganic salts is induced. These phenomena cause clogging at the discharge orifice, which should be avoided with the utmost of care.
In order therefore to eliminate such disadvantageous effects, it is necessary to control the inorganic salts concentration within a predetermined range when producing the ink (in general, it is to be limited to 0.5 wt. % or less with respect to the total ink composition). This control is indispensable when the dyestuff available in general market, which contains therein inorganic salts as impurities, is used for preparation of the ink for the ink jet recording as well as for the writing implements.